1. Field of the Invention
The present invention relates to ultrasound imaging. More particularly, although not exclusively, the present invention relates to high frequency ultrasound imaging for use in medical applications.
2. Problems in the Art
Ultrasound imaging is widely used in non-destructive evaluation and testing, including medical applications. In ultrasound imaging, typically a probe having ultrasound transducers is used to create sounds and then listen for echos. The received signals of the echos are then analyzed or otherwise processed to create images or for other analysis.
The frequency used is related to the depth of the imaging, so the frequency of the ultrasound used will vary from application to application. For example, high frequency applications such as frequencies over 30 MHz have been found to be useful in various medical applications such as, but not limited to, ophthalmology, dermatology, intravascular imaging, small animal imaging, and intraoperative/laproscopic applications (F. S. Foster, C. J. Pavlin, K. A. Harasiewicz, D. A. Christopher, and D. H. Turnbull, xe2x80x9cAdvances in ultrasound biomicroscopy,xe2x80x9d Ultrasound Med. Biol., vol. 26, pp. 1-27, 2000). The frequency is proportional to the resolution, therefore these higher frequencies also result in the ability to resolve small structures.
There are various types or configurations of ultrasound transducers. For example, mechanically scanned single element transducers have been used at high frequencies (i.e. frequencies greater than 30 MHz). In addition, linear arrays of ultrasound transducers or elements have been used, typically at much lower frequencies. Using multiple ultrasound elements increases the speed at which imaging can occur. Imaging arrays capable of operation at high frequencies are not available. Instead, mechanically scanned single-element transducers are used to acquire the pulse-echo data at this frequency. Improved performance could theoretically be obtained with an array, however, the high frequency puts a physical limitation on the size of the device.
In ultrasound arrays, typically the elements are spaced at half wavelength intervals for phased arrays and at full wavelength intervals for linear arrays. The center to center spacing of the elements in these arrays is known as pitch. To achieve high frequencies, according to prior art methodologies, the element spacing must be reduced. However, current interconnect and fabrication techniques do not permit element spacing of less than 50 micrometers. In addition, the size of the transducers must also decrease. Since capacitance and frequency are inversely related, high frequencies lead to low capacitance of the elements and low signal-to-noise ratios. Therefore, imaging arrays operating at high frequencies have not been used. In addition, other problems in implementation would occur. These include the cost and complexity of a beamformer with high channel counts that is also capable of performing appropriately despite electrical and acoustic cross talk considerations. Therefore, problems remain.
An ideal solution would be to decrease the number of active channels, to increase the width of the elements, to increase the center-to-center element distance (pitch), to increase the separation between elements, and to accomplish these goals while still obtaining sampling rates and signal-to-noise ratios suitable for imaging.
Therefore, it is a primary object of the present invention to provide for an ultrasound-imaging array that improves upon the state of the art.
It is a further object of the present invention to provide an ultrasound-imaging array that allows for a decreased number of active channels.
Another object of the present invention is the provision of an ultrasound-imaging array that allows the width of the elements to increase.
Yet another object of the present invention is an improved ultrasound-imaging array that allows the center-to-center element distance to increase.
A still further object of the present invention is to provide an ultrasound-imaging array that allows for increased separation between elements.
Another object of the present invention is to provide an improved ultrasound-imaging array that provides for sampling rates and signal to noise ratios suitable for imaging.
A still further object of the present invention is an improved ultrasound-imaging array that is capable of use at frequencies at or above 30 MHz.
These and other objects, features, or advantages of the present invention will become apparent from the Specification and Claims.
According to the present invention, in order to overcome problems in the art, a motion mechanism is combined with an imaging array. The motion mechanism may be an actuator. The actuator moves the imaging array. The actuator may be moved in short, precise, incremental steps to increase spatial sampling density. Alternatively, the actuator may move continuously as imaging occurs.
One aspect of the present invention relates to a device for ultrasound imaging at high frequencies with improved spatial sampling. The device includes a plurality of ultrasound imaging elements each having a pitch defined by the center-to-center spacing of the ultrasound imaging elements. The device also includes an actuator operatively connected to the plurality of ultrasound imaging elements and adapted to move the plurality of ultrasound imaging elements over a distance significantly less than the total length of the array and for the expressed purpose of enabling increased spatial sampling. The distance may be defined as a series of incremental steps which the actuator moves. Alternatively, the actuator""s movement can be continuous instead of discrete. Preferably, a synthetic aperture software beamformer is used to reconstruct an image from the pulse-echo data.
Another aspect of the present invention involves a method. According to this aspect of the present invention, the method of ultrasound imaging includes transducing a plurality of signals from a plurality of ultrasound imaging elements, moving the plurality of ultrasound imaging elements an incremental distance, and repeating the steps of transducing and moving one or more times. The total distance moved is the sum of each incremental distance and is significantly less than the total length of the array. Alternatively, the actuator""s movement can be continuous instead of discrete. The movement enables increased spatial sampling and allows an array with a large pitch, defined by the center-to-center spacing of the ultrasound imaging elements, to mimic the performance achieved with a much smaller pitch. Pulse-echo data is obtained at each position and this data is then used to create an image, such as through synthetic aperture processing.
The present invention creates a number of advantages. It allows for imaging at high frequencies. It simplifies the hardware needed through lowering the number of active channels required. Further, this approach can use imaging elements of dimensions that are within current day manufacturing processes.